This invention relates to the formation of segments for substantially spherical containers and the like.
In the art of handling liquified natural gas and other similar materials, the gas is often stored in liquid phase in very large generally spherical containers fabricated from aluminum. These containers comprise a pair of end caps and a plurality of segmental plates which are welded together along seams which, in effect, define latitude and longitude lines.
Heretofore, it has been found to be very difficult to accurately join the segments, because of their curved nature and because of their relatively large size, such as 12 feet .times. 50 feet. It has been difficult to form the segments accurately, since a segment presents a compound curvature and it is difficult to know in forming exactly where its edge is. The resultant tolerances for the sphere have therefor been larger than desired.
The present invention solves the previous forming problems. In accordance with the invention, a flat metal plate is first formed into a suitable segment of a large generally spherical body. It is then properly positioned on a horizontal cradle and its edges cut vertically as if from infinity, i.e. so that they are all parallel. A cutter then traverses the pre-cut edge to form the proper contour for welding. The pre-cut edge itself forms an accurate fixed reference and cooperates with guides on the face of the curved plate to keep the axis of the milling cutter tool substantially perpendicular to the surface of the plate at the point of milling cutter contact. When all segments are so made and then joined, the resultant generally spherical body will be within substantially closer tolerances.